U.S. Pat. No. 5,065,527 discloses a positive drive length measuring apparatus for accurately measuring the length of a continuously produced product, e.g. cable, hose, rope, tube, strip, wire, fiber and etc, for pulling a product through a process and for identifying precision lengths for cut-off of the product. This apparatus has first and second shafts which are aligned and spaced apart from each other such that first and second inflatable and pliable members attached to first and second shafts engage each other to define a common chord which engages the product as it moves along the common chord. An encoder responsive to the rotation of the first shaft generates discrete signals which are communicated to a counter to provide an indication of the length and other information with respect to the product. Unfortunately through experience it has been determined that in the manufacture of the first and second inflatable and pliable members significant variations can occur in the actual diameter of such inflatable and pliable members even though they are sold and identified as having the same diameter. This size difference is explained as being a nominal tolerance in the diameter occurring as a result of differences in manufacturing molds for such inflatable and pliable members. Once the length of the common chord is established, this apparatus functions in an acceptable manner as long as the first and second diameters and correspondingly the circumference of the first and second inflatable and pliable members remain substantially identical after calibration of the encoder.